Double base propellant compositions which contain nitrocellulose, nitroglycerin, selected organic or inorganic salts for ballistic or stabilizer functions, and additives such as carbon black are generally considered normal double base propellant compositions. When an inorganic oxidizer salt is added to the formulation the term modified double base or composite double base is generally employed. Other compounds such as coating agents may be used with the inorganic oxidizer salt to achieve the desired properties in the finished propellant. The composite propellant compositions may include metal fuel along with other compounds which serve as ballistic modifiers, plasticizers, or processing aids. The propellants can be cast, extruded, or rolled depending on the formulation and the desired shape required for the cured propellant which is referred to as a propellant grain.
The burning rate curve, where burning rate is plotted against puressure, provides useful information to the propulsion engineer in designing a motor case for a particular mission. Also, the burning rate exponent of a propellant is another indicator to the artisan what advantages or disadvantages a propellant may offer. When the burning rate exponent is high the design problems for the motor case are more complex. Some propellants with an almost flat burning rate curve will have a low burning rate exponent. The motor case for a rocket motor using a plateau or mesa type propellant (i.e., where the burning rate is fairly constant over a wide pressure range) is quite different and less complex to design than where the motor case chamber pressure is extremely high, the propellant burning rate high, the the propellant burning rate exponent high. The grain design or construction can also be tailored to produce the desired burning rate pressure relationship.
Desirable for use in small diameter rocket motors would be a propellant with the highest burning rate at elevated pressures while having a lower burning rate exponent. Also desirable is a propellant having the lower burning rate exponent and one not susceptible to resonance burning.
Therefore, an object of this invention is to provide a propellant composition having a lower pressure exponent with a higher burning rate at elevated pressure.
Another object of this invention is to provide a propellant composition which is not susceptible to resonance burning.